Softball is a sport that requires speed, agility, and lower-body power to be successful. Accordingly, strength and conditioning programs have focused on improving speed and lower-body power, which are beneficial to players performing softball-related tasks. The purpose of this study was to determine the correlation between absolute and relative lower-body strength to performance measures among female collegiate softball players. Archived data collected during pre-season performance testing for twenty-one (n = 21) NCAA Division II collegiate softball players was used for this analysis. Measurements included countermovement jump (CMJ), broad jump (BJ), linear speed (LS), 505 test for change of direction speed (COD), and shuttle runs. Absolute lower body strength (ALBS) was measured using a 3-repetition maximum hex-bar deadlift (HBDL) and body weight was used to calculate relative lower body strength (RLBS) of each player. Pearson's correlation coefficients were used to relate measures of lower body strength to each performance test. Significant (p ≤ 0.05) large to moderate correlations were discovered between RLBS and COD (505L: r = -0.59, 505R: r = -.63), 300 yard (yd) shuttle run time (trial 1: r = -0.47, trial 2: -0.50), and lower-body power (CMJ: r = 0.48, BJ: r = 0.52). ALBS was correlated only to the BJ (r = 0.43). The results suggest that relative strength is related more with COD, shuttle run, and lower-body power when compared to absolute strength. Therefore, strength and conditioning professionals should consider measures of RLBS when administering softball specific tests for developing and implementing a successful strength program in collegiate softball.

Lacrosse players are required to perform multiple sprints and changes of direction over the course of a game. These skills are reliant on the ability to rapidly produce lower-body force to be successful. Currently, little research examining the relationship between specific performance indicators and relative strength within this population exists. The purpose of this study was to investigate relationships between measures of lower-body strength and power to sprinting and change of direction speed (CODS) among male lacrosse players. Archived data for (n= 18) NCAA Division II male lacrosse athletes were used for this analysis. Lower-body strength was assessed using a one-repetition maximum back squat. Power was assessed using a countermovement jump (CMJ), squat jump (SJ), and standing long jump (SLJ). Sprint speed at 10 and 30 yds (i.e., 9.14 and 27.43 m) and CODS (i.e., T-Test (TT) and modified T-Test (MTT) were also assessed. Pearson’s correlation was used to determine relationships between lower-body strength and power to sprint speed and CODS. Significant relationships (r = -0.51 - -0.64, p ≤ 0.05) were discovered between all measures of power and CODS, as well as SLJ and sprint speed (r = -0.51; p = 0.05 and -0.67; p ≤-0.01, respectively). No significant relationships between relative strength and any measures of sprint speed or CODS were discovered. Although relative strength was not directly related to sprint speed or CODS performance, it may indirectly affect these measures based on its relationship to power, and power’s relationship to sprint and CODS performance.

Background: Falls and decreased physical function increase markedly with age and result in injury, hospitalization, and premature death. Emerging studies show potential benefits of supplemental cocoa extract on physical performance, including grip strength and walking speed in older adults. However, there are no large, long-term randomized controlled trials of effects of supplemental cocoa extract on falls, muscle performance, and/or fallrelated injuries. Methods: The COcoa Supplement and Multivitamin Outcomes Study (COSMOS) is a double-blind, placebocontrolled, 2 x 2 factorial trial investigating effects of supplementation with cocoa extract (500 mg/d, including 80 mg (-)-epicatechin) and/or a multivitamin on prevention of cardiovascular disease and cancer in 21,442 women (>= 65 years) and men (>= 60 years). COSMOS: Effects on Falls and Physical Performance is an ancillary study to COSMOS that will clarify effects of cocoa extract and/or multivitamin supplementation on falls, physical performance, and incident fracture outcomes in older adults. Injurious fall(s) resulting in healthcare utilization and recurrent falls were regularly assessed by follow-up questionnaires in the overall cohort. Incident fractures were also assessed by annual questionnaires. Circumstances surrounding falls and any fall-related injuries will be confirmed by medical record review. Effects of the interventions on 2-year changes in physical performance measures (grip strength, walking speed, and the Short Physical Performance Battery) will be tested in a clinic sub-cohort (n = 603). Conclusion: Results from this ancillary study will determine whether supplemental cocoa extract slows agerelated declines in physical performance and decrease injurious and recurrent falls and fall-related injuries and fractures that are major public health problems in older adults.

The purpose of this study was to determine if significant relationships exist between absolute and relative lower-body power and selected measures of speed among male and female collegiate basketball players. Archived performance testing data from 29 (male = 14; female = 15) NCAA division II collegiate basketball players were used for this analysis. These measures included lane agility, 10-yard sprint, and shuttle run time (sec). A Pearson's correlation coefficient was used to determine if significant relationships existed between measures of lower-body power and linear sprint time, change of direction speed (CODS), and shuttle performance. Statistical significance was set a priori at p ≤ 0.05. A significant large correlation was found between absolute power and lane agility (r = 0.54, p = 0.05) among male players. No significant correlations were found between absolute or relative power for 10-yard sprint times, lane agility, or shuttle run performance (p > 0.05). Females showed no significant correlations between relative power and lane agility (r = -0.25, p = 0.37) or 10-yard sprint (r = -0.47, p = 0.08), but did show a significant large correlation (r = -0.64, p = 0.01) between relative power and shuttle run performance. Generating high amounts of relative power is vital in intermittent team sports such as basketball. In particular, this study provided evidence that relative power in female collegiate basketball players is significantly related to shuttle run ability.

There is evidence to suggest that aquatic plyometric training (APT) may be an effective and safer alternative to traditional land-based plyometric training (LPT) when training to increase jump performance. The aim of this review was to critically examine the current literature regarding the effects of APT vs. LPT on jump performance in athletic populations. Key terms were employed in five separate databases to complete the current review. Available articles were screened for inclusion and exclusion criteria to determine which studies were deemed eligible for review. Outcome measure in these studies included those assessing lower extremity power and jump performance (i.e., drop jumps, broad jumps, sergeant jumps, repeated countermovement jumps, and vertical jumps). All but one of the studies included in this critical review showed significant improvements in jump performance after LPT and APT interventions. Both LPT and APT groups experienced similar increases in jump performance and lower-body power, pre- to post-test, in the majority of the studies examined in this review. LPT and APT have the ability to improve lower extremity explosive strength and jump performance within athletic populations. Improvements in lower body power may improve overall athletic performance. Observations from this review may be used by sport coaches, strength coaches, and athletes alike to weigh the pros and cons of both forms of plyometric training. Observations from this review may also be used to weigh the pros and cons of APT over LPT in terms of reducing risk of injury.

Simulated fire ground scenarios (SFGS) provide firefighters with an opportunity to maintain skills, receive feedback, and optimize performance. Although there is extensive research on heart rate (HR) changes in the firefighter population, few examine the differences between positions. Firefighters are primarily responsible for fire suppression and control (23), officers for emergency operations and organizational management, paramedics for providing on-scene emergency medical care, and drivers are responsible for driving the fire apparatus. Utilizing HR analysis to quantify the physical demands of SFGS among firefighting crews by position. Sixty-seven male (age: 38.97 ± 9.17; ht: 177.99 ± 6.45 cm. wt: 88.83 ± 13.55 kg) firefighters (FF) participated in this investigation. FF crews performed two SFGS involving the suppression and control of a structural fire. Participants were outfitted with heart rate (HR) monitors and average heart rate (HRavg) and maximum heart rate (HRmax) data were collected for each of the two SFGS. Significant differences were observed for Age (P = 0.01), APMHR (P = 0.01), HRmax1 (P = 0.04), and HRmax2 (P = 0.04) in which firefighters had higher values for Age-predicted maximal heart rate (APMHR), HRmax1, HRmax2 compared to the officers. SFGS can be very physically demanding events that may elicit maximal or near maximal HR responses regardless of position. Based on the metabolic demands of these events and the individual firefighter's capabilities, this information can be used to develop resistance training and conditioning programs that optimize performance at maximal or near maximal heart rates.

The purpose of this investigation was to examine the immediate and acute vertical jump performance responses throughout and following two different free-weight back squat exercise protocols. Fifteen resistance-trained women (mean ± SD: age = 21.8 ± 0.9 years; height = 164.6 ± 8.4 cm; mass = 68.5 ± 9.2 kg) performed vertical jumps before (Pre), immediately after each set (S1-S5), and up to 20 minutes post squat exercise (Post0-Post20) of either a power-endurance (PE; 5×16 at 40% 1-RM) or controlled heavy (CHP; 5×8 at 80%) protocol. Participants' jump height (JH), mean (MP), peak power (PP), mean (MV) and peak velocity (PV) were measured using a linear position transducer. 2-way repeated measures ANOVAs were run for all dependent variables. In the case of the violation of sphericity Greenhouse-Geisser results were reported. No significant intensity × time interactions were observed for any of the variables (p = 0.30-0.87). Main effects for time were observed (p ≤ 0.001, ηp2 = 0.52) for MP and MV, which were significantly lower than Pre at S2 through S5-Post0 (p = 0.001-0.02) time points. Additionally, main effects for time were observed (p ≤ 0.001, ηp2 = 0.43) for PP and PV, which were significantly lower than Pre at all time points (p = 0.001-0.03) with the exception of Post10 (p = 0.17-0.21). Lastly, JH was significantly lower than Pre for all time points (p ≤ 0.001-0.02) except for Post5 (p = 0.13) and Post10 (p = 0.25). This study suggests overall training volume and not training-load could have attributed to the similar fatigue and recovery-related responses that were observed. The present findings suggest that vertical jump performance may be negatively affected following moderate to heavy exercise for up to 20 minutes.

INTRODUCTION: Body composition (BC) measurements are used to determine qualification for enlistment and to ensure active members are meeting standards. Although there is extensive research on BC in active-duty military, very few have examined ROTC cadets. The purpose of this study was to identify and quantify differences in BC between freshman/sophomore [underclass (UND)] and junior/senior [upperclass (UPP)] ROTC cadets by using bioelectrical impedance spectroscopy (BIS). METHODS: UND ( N = 21) and UPP ( N = 15) Air Force ROTC cadets volunteered for this study. BIS was used to measure fat mass percentage (FM%), fat free mass percentage (FFM%), total body water percentage (TBW%), extracellular fluid percentage (ECF%), and intracellular fluid percentage (ICF%). Separate one-way ANOVAs were run between UND and UPP for all dependent variables with a Bonferroni correction factor. Additionally, a Pearson correlation between abdominal circumference (AC) and FM% was conducted. RESULTS: No significant differences were observed between the UND and UPP groups’ BMI. However, significant differences were observed for ECF%, ICF%, TBW%, FFM%, and FM% in which the UPP had a higher TBW%, ICF%, FFM%, and a lower ECF% and FM% compared to the UND. CONCLUSIONS: This study observed significant differences in BC across class ranks in ROTC cadets. Findings from this study suggest that due to an increased exposure to ROTC training, UPP cadets have a more ideal body composition (FFM% and FM%) when compared to UND cadets. Johnson QR, Mackey CS, Muddle TD, Smith DB, DeFreitas JM. Body composition comparison of upper- and underclass Reserve Officers Training Corps cadets . Aerosp Med Hum Perform. 2019; 90(9):813–818.

Abstract Magrini, MA, Colquhoun, RJ, Sellers, JH, Conchola, EC, Hester, GM, Thiele, RM, Pope, ZK, and Smith, DB. Can squat jump performance differentiate starters vs. nonstarters in division I female soccer players? J Strength Cond Res 32(8): 2348–2355, 2018—Although soccer is predominately an endurance sport, high velocity movements may be an important indicator of athletic success. The purpose of this investigation was to establish whether squat jumps (SJs) can differentiate starters from nonstarters with a female collegiate division I soccer team. Eighteen female division I soccer athletes were separated into 2 groups: 9 starters (age: 19.5 ± 1.0; mass = 64.8 ± 11.5 kg; height = 167.5 ± 7.7 cm; games started = 18.2 ± 4.7; and minutes played = 1633.8 ± 478.2 minutes) and 9 nonstarters (age: 19.4 ± 1.4 years; mass = 63.3 ± 4.2 kg; height = 164.7 ± 6.8 cm; games started 0.7 ± 1.3; and minutes played 158.2 ± 269.3 minutes). Each athlete performed 3 maximal SJs at a starting knee angle of 110° without arm swing. Each participant's SJ height, mean power (MP), peak power (PP), mean velocity (MV), and peak velocity (PV) were measured during each attempt by a linear position transducer. No statistically significant differences (p ≥ 0.05) in MP and PP between the starters and nonstarters were observed. However, starters performed significantly better than nonstarters in SJ height (p = 0.002), MV (p = 0.025), and PV (p = 0.015). In addition, SJ height was strongly correlated with MV (r = 0.628) and PV (r = 0.647). These findings suggest that SJ height, MV, and PV may be important variables for discriminating differences between starters and nonstarters in division I female soccer athletes and a strong indicator of explosive performance.

OBJECTIVE: The purpose of this investigation was to examine the effects of two back squat exercise protocols on recovery responses of maximal unloaded velocity (Vmax) and angular acceleration (ACC240, ACC500) of the knee extensors. METHODS: Fourteen resistance-trained men (mean +/- SD: age = 22.07 +/- 2.6 years) and sixteen women (age = 21.75 +/- 1.0 years) performed maximum voluntary contractions at 240 degrees . s(-1) and 500 degrees . s(-1) before (Pre) and after (Post0-Post30) a squat exercise using either a power-endurance (PE) (5 x 16 at 40% one-repetition maximum), or controlled hypertrophic (CH) (5 x 8 at 80% one-repetition maximum) protocol. RESULTS: There was a significant main effect for time (p <= 0.001) in which ACC240 was greater at Pre compared to Post0, Post15 and Post30 (p = 0.001-0.023), no differences were observed at Post7 (p = 0.186). For ACC500, all post-recovery time phases (Post0-Post30) were lower than Pre (p <= 0.001). A sex x intensity x time (p = 0.040) interaction was observed for Vmax where only the CH protocol was significantly decreased (p = 0.019) for the males at Post0. All other post-recovery time phases for Vmax were lower compared to Pre for both protocols (p = 0.002-0.025). CONCLUSIONS: Similar fatigue and recovery-related responses were observed between genders in regards to ACC and Vmax following volume-matched PE and CH squat protocols. Knowing that a variety of populations implement compound movements into their resistance training routines, the present findings suggest that ACC and Vmax may be negatively affected following moderate to heavy exercise for up to 30 minutes. Thus, assessing ACC and Vmax post-exercise may be a valuable measure in identifying the residual consequences of fatigue over a short-term recovery period.

The selection of epoch lengths affects the time and frequency resolution of electromyographic (EMG) and mechanomyographic (MMG) signals, as well as decisions regarding the signal processing techniques to use for determining the power density spectrum. No previous studies, however, have examined the effects of epoch length on parameters of the MMG signal. The purpose of this study was to examine the differences between epoch lengths for EMG amplitude, EMG mean power frequency (MPF), MMG amplitude, and MMG MPF from the VL and VM muscles during MVIC muscle actions as well as at each 10% of the time to exhaustion (TTE) during a continuous isometric muscle action of the leg extensors at 50% of MVIC. During the MVIC trial, there were no significant (p > 0.05) differences between epoch lengths (0.25, 0.50,1.00, and 2.00-s) for mean absolute values for any of the EMG or MMG parameters. During the submaximal, sustained muscle action, however, absolute MMG amplitude and MMG MPF were affected by the length of epoch. All epoch related differences were eliminated by normalizing the absolute values to MVIC. These findings supported normalizing EMG and MMG parameter values to MVIC and utilizing epoch lengths that ranged from 0.25 to 2.00-s.

BackgroundCompression garments (CGs) have increased in popularity within recreational and competitive athlete populations. PurposeThe purpose of this study was to examine the effect of CGs on physiological, performance, and perceptual measures while running on uneven terrain at higher altitude. MethodsNine recreationally active males participated in two trail running sessions (7 km: uphill section 3.5 km, and downhill section 3.5 km).In the first session, participants completed the 7 km trail while wearing regular athletic clothing.Seven days later, participants then completed the same 7 km trail wearing CGs.Physiological and performance measures were collected at the baseline, during the trail run, immediate post-run, and 24, 48, 72 hours after the trail run. ResultsResults showed no significant differences in time to completion (p=≥0.05).However, there were significant differences in physiological load (p=0.04),training load (p=0.01),average physiological intensity (p=0.05), and estimated caloric expenditure (p=0.02) between trials.Significant improvement in vertical jump height and peak anaerobic power in watts (p=0.04),isometric strength (p=0.03), and post-exercise pain ratings at 48 (p=0.01) and 72 (p=0.038)hours post exercise were found under the CG condition. ConclusionAlthough there were no differences in time to complete the runs in both conditions (with and without CGs), the significant differences in the physiological measures suggests that the CGs may have an ergogenic effect when participating in trail running activities at a higher altitude.Therefore, wearing CGs may increase exercise efficiency and capacity, leading to a possible increase in recovery from training and activity.

Objective: The purpose of this study was to determine the intratester and intertester reliability of three common methods of assessing hydration; urine color chart (UCC), dipstick reagent strip (DRS) and refractometer (REF). Methods: Twenty-three male collegiate wrestlers (n = 23, age = 20.09 ± 1.35, weight = 78.73 ± 11.25 kg, height = 174.49 ± 7.23 cm) provided urine samples on three separate occasions totaling 69 samples (n = 69). Samples were analyzed with repeated measures by three testers, three trials, and three separate methods of assessment. Results: All methods had very high intertester reliability as demonstrated by Cronbach’s Alpha coefficients; DRS (r = .985), UCC (r = .973) and REF (r = .968). Intraclass correlation coefficient ranges were also very high; DRS .983 .994, UCC 964-.983, and REF .829-.996. Conclusions: The three modes of urine hydration assessment are highly reliable, and are a practical, noninvasive method to evaluate hydration status in the field.

OBJECTIVE: We examined the relationships among and differences between muscle size and strength, specific tension (MQST), echo intensity (MQEI), and functional performance in physically active younger and older women. METHODS: Measurements included maximal voluntary isometric knee extension contrac tions (MVICs), maximal velocity sit-to-stand (STS) movements, and muscle cross sectional area (mCSA), MQST, and MQEI of the rectus femoris (RF). RESULTS: There were no differences in MQST (p= 0.96) or physical activity levels (p= 0.29). MQST and MQEI were not related in the younger women, but were related in the older women (r= 0.50). MVIC was related to mCSA (r= 0.75) in the older women, but was not significantly related to MQST or MQEI in either age group. DISCUSSION: Physical activity may maintain MQST in aging. We suggest that studies examining changes in skeletal muscle with aging utilize both traditionally calculated muscle quality (specific tension) and ultrasound EI.

Although soccer is predominately an endurance sport, high velocity movements may be an important indicator of athletic success. The purpose of this investigation was to establish whether squat jumps (SJ) can differentiate starters from non-starters with a female collegiate division I soccer team. Eighteen female division I soccer athletes were separated into two groups: 9 starters (age: 19.5 ± 1.0; mass = 64.8 ± 11.5 kg; height = 167.5 ± 7.7 cm; games started = 18.2 ± 4.7; minutes played = 1633.8 ± 478.2 min) and 9 non-starters (age: 19.4 ± 1.4 years; mass = 63.3 ± 4.2 kg; height = 164.7 ± 6.8 cm; games started 0.7 ± 1.3; minutes played 158.2 ± 269.3). Each athlete performed 3 maximal SJs at a starting knee angle of 110° without arm swing. Each participant's SJ height, mean power (MP), peak power (PP), mean velocity (MV), and peak velocity (PV) were measured during each attempt by a linear position transducer (LPT). No statistically significant differences (p ≥ 0.05) in MP and PP between the starters and non-starters were observed. However, starters performed significantly better than non-starters in SJ height (p = 0.002), MV (p = 0.025), and PV (p = 0.015). Additionally, SJ height was strongly correlated with MV (r = 0.628) and PV (r = 0.647). These findings suggest that SJ height, MV and PV, may be important variables for discriminating differences between starters and non-starters in division I female soccer athletes and a strong indicator of explosive performance.

The purpose of the present study was to examine the effects of electrode placements centered over and offset from the innervation zone (IZ) with different interelectrode distances (IED) on the time and frequency domain parameters of the electromyographic (EMG) signal during a fatiguing submaximal, isometric workout. 11 adults performed an isometric leg extension muscle action at 50% maximal voluntary isometric contraction (MVIC) to exhaustion. Electromyographic amplitude and frequency parameters were determined from electrode placements with different IED centered over, at proximal offset, at distal offset, and away from the IZ at 10, 50, and 100% of the time to exhaustion using an electrode array. There were greater absolute EMG amplitude and lower absolute EMG frequency for electrode placements over and offset from the IZ, but lower absolute EMG amplitude over than offset from the IZ regardless of IED at each time-point during the time to exhaustion. The absolute EMG frequency values were affected by the location relative to the IZ and IED of the electrode placements, and were greater for distal offset vs. proximal offset electrode placements at each time-point. Normalization of the EMG amplitude and EMG frequency values to MVIC eliminated differences due to IED and electrode placements during the fatiguing workout.

The quality of skeletal muscle has been identified as an important factor that is used to describe intramuscular changes associated with muscle function in aging. Traditionally, muscle quality (MQ) has been calculated as maximal muscle strength expressed per unit of muscle mass. More recently, however, the echo intensity (EI) of skeletal muscle ultrasound images has been used as a surrogate measure of muscle quality. PURPOSE: The purpose of this study was to examine the relationships among and differences between commonly-used measures of MQ and functional performance in younger (YW) and older women (OW). METHODS: 15 YW (mean ± SD: 22 ± 2 yrs) and 15 OW (74 ± 5 yrs) completed this study. Muscle cross section area (mCSA) and EI of the rectus femoris were measured from ultrasound scans at the midpoint of the thigh. Each participant completed two maximal voluntary isometric knee extension contractions (MVICs) to determine MVIC strength. Each participant also completed three maximal velocity sit-to-stand movements, during which power and movement velocity were measured. MQ was calculated as MVIC strength ÷ mCSA. Independent samples t-tests were used to analyze differences between YW and OW and Pearson’s correlation coefficients were also used to analyze the relationships among the dependent variables in the YW and OW. RESULTS: MVIC strength (166 ± 37 vs 105 ± 28 Nm), mean velocity (0.6 ± 0.1 vs 0.4 ± 0.1 m/s), peak velocity (0.9 ± 0.2 vs 0.7 ± 0.1), mean power (435 ± 81 vs 299 ± 57 W), peak power (1070 ± 265 vs 597 ± 127 W) were greater and EI (39 ± 8 vs 52 ± 10 au) was lower in the YW than OW, respectively. There was no difference in muscle quality (p = 0.96). EI and MQ were not significantly related (r = 0.12) in the YW, but were significantly related in the OW (r = 0.54). EI was inversely related to mCSA in the YW (r = -0.53) and OW (r = -0.54). In addition, MVIC was significantly related to mCSA (r = 0.75) in the OW, and was not significantly related to EI or MQ in either the YW or OW. CONCLUSION: There were age-related differences in muscle strength, muscle size, echo intensity, and functional performance, but no age-related difference in traditionally measured MQ. EI was related to MQ in the OW, but not the YW. Although EI has been used as a surrogate for MQ, these data suggest that MQ and EI may reflect different qualities of skeletal muscle in aging.

Previous authors have examined the isokinetic rapid velocity capacities of young and old individuals. However, these approaches may not be applicable for all individuals, especially those who are older and more frail. Alternatively, the sit-to-stand (STS) test may be a more practical and functionally-relevant assessment tool for examining PV and AV in these types of individuals. Consequently, it may be of great value to examine the reliability of PV and AV using a portable linear transducer in conjunction with the STS. PURPOSE: To determine the reliability of PV and AV measurements during STS assessments using a linear transducer. METHODS: Sixteen healthy males (mean±SD: age=24±4yr; height=177±7cm; mass 86±19kg) participated in this investigation. Participants visited the laboratory 2 times, separated by 2-7 days at the same time (±2hr). For each visit, participants performed 3 STSs from an adjustable table at 90° (STS90) and 120° (STS120) of knee flexion in a randomized order. To determine PV and AV, the testing device was attached to the posterior portion of a belt fastened around the participants’ waistline. Participants performed all STSs with feet shoulder width apart and hands positioned on the hips. For each STS, participants were asked to stand-up as explosively as possible. Reliability for PV and AV during the STS90 and STS120 were determined using the intraclass correlation coefficient (ICC, model 2,1) and standard error measurement (SEM). Systematic variability was examined using separate one-way repeated measures analyses of variance (ANOVAs). RESULTS: The ANOVAs indicated no systematic variability in PV and AV across trials (P>0.05). The ICCs and SEM values expressed as a percentage of the mean for PV ranged from 0.796-0.921 and 6.277-6.454%. Additionally, ICCs and SEM values for AV ranged from 0.361-0.727 and 14.30-19.98%. CONCLUSIONS: The results of the present investigation reveal that a portable linear transducer may be highly consistent and equally reliable for assessing PV and AV during STS measurements. These findings demonstrate portable devices may be a relevant tool in assessing velocity capacities during a practical STS movement. Future researchers or current practitioners may consider utilizing such devices to assess functional performance in older community-dwelling individuals.

Abstract Smith, CM, Housh, TJ, Herda, TJ, Zuniga, JM, Camic, CL, Bergstrom, HC, Smith, DB, Weir, JP, Hill, EC, Cochrane, KC, Jenkins, NDM, Schmidt, RJ, and Johnson, GO. Time course of changes in neuromuscular parameters during sustained isometric muscle actions. J Strength Cond Res 30(10): 2697–2702, 2016—The objective of the present study was to identify the time course of changes in electromyographic (EMG) and mechanomyographic (MMG) time and frequency domain parameters during a sustained isometric muscle action of the leg extensors at 50% maximal voluntary isometric contraction. The EMG and MMG signals were measured from the vastus lateralis of 11 subjects to identify when motor unit activation strategies changed throughout the sustained isometric muscle action. The EMG amplitude (muscle activation) had a positive linear relationship (p = 0.018, r 2 = 0.77) that began to increase at the initiation of the muscle action and continued until task failure. Electromyographic frequency (motor unit action potential conduction velocity) and MMG frequency (global motor unit firing rate) had negative quadratic relationships (p = 0.002, R 2 = 0.99; p = 0.015, R 2 = 0.94) that began to decrease at 30% of the time to exhaustion. The MMG amplitude (motor unit activation) had a cubic relationship (p = 0.001, R 2 = 0.94) that increased from 10 to 30% of the time to exhaustion, then decreased from 40 to 70% of the time to exhaustion, and then markedly increased from 70% to task failure. The time course of changes in the neuromuscular parameters suggested that motor unit activation strategies changed at approximately 30 and 70% of the time to exhaustion during the sustained isometric muscle action. These findings indicate that the time course of changes in neuromuscular responses provide insight into the strategies used to delay the effects of fatigue and are valuable tools for quantifying changes in the fatiguing process during training programs or supplementation research.